New energy sending-out system and method based on low-frequency SLCC back-to-back

Abstract

The invention relates to the technical field of new energy, and discloses a low-frequency SLCC back-to-back based new energy sending system and method.The new energy station is used for generating low-frequency alternating current, and the low-frequency alternating current is transmitted to a back-to-back converter station through a low-frequency power transmission line; the rectifier station is used for converting low-frequency alternating current transmitted by the low-frequency power transmission line into direct current, and the direct current is transmitted to the inverter station through a direct current line; the inverter station is used for converting direct current transmitted by the direct current line into power frequency alternating current, and the power frequency alternating current is transmitted to a receiving end power grid. According to the technical scheme provided by one or more embodiments, low-frequency power transmission and direct-current power transmission are combined, and large-scale new energy efficient delivery is achieved.

Description

Technical Field

[0001] The present application relates to the field of new energy transmission technology, and in particular to a new energy transmission system and method based on low-frequency SLCC back-to-back. Background Art

[0002] With the maturity of new energy power generation technology, my country's new energy installed capacity has increased rapidly, and it has shown the characteristics of from nearshore to offshore, from shallow water to deep water, and from small-scale demonstration to large-scale centralized development. The system support capacity of new energy units is relatively weak. Conventional DC transmission technology is no longer applicable in the scenario of high-proportion new energy long-distance transmission. SVG is configured on the valve side of the transformer. The converter composed of it and LCC is called SLCC, which can compensate for the reactive power consumption and harmonic current during the operation of LCC. The system does not need to be additionally configured with AC filters / parallel capacitors, which can effectively solve problems such as AC overvoltage / low voltage ride-through and receiving-end commutation failure. Compared with flexible DC transmission, it occupies a smaller area and has stronger economy. SLCC has received widespread attention in recent years and has been applied in engineering. However, for scenarios such as offshore wind power that require the weight and volume of the sending-end converter station, there is still a lot of room for improvement in the lightweighting of SLCC.

[0003] In addition to DC transmission, low-frequency transmission also has significant advantages in the long-distance transmission of large-scale renewable energy. The low-frequency transmission system uses a lower frequency to transmit electric energy. Compared with the industrial frequency system of the same voltage level, its line transmission capacity has been greatly improved. It has received extensive attention in the field of efficient collection and transmission of renewable energy, including medium / long-distance offshore wind power, onshore wind power in remote areas of "Shagohuang", photovoltaic power generation and large-scale hydropower transmission. In terms of lightweight, low-frequency transmission also has significant technical advantages over DC transmission. New energy stations can directly convert electrical energy into low-frequency AC power for transmission, without the need to establish a sending-end converter station on the new energy side, which greatly improves the energy utilization efficiency. How to combine the technical advantages of low-frequency transmission and DC transmission to achieve large-scale efficient and reliable transmission of new energy is the original intention of this invention and the core problem that it focuses on solving. Summary of the invention

[0004] One or more embodiments of the present disclosure provide a new energy delivery system and method based on low-frequency SLCC back-to-back, which can realize large-scale, efficient and reliable delivery of new energy.

[0005] In order to achieve the above objectives, the main technical solutions adopted by this disclosure include: On the one hand, the present disclosure provides a new energy transmission system based on low-frequency SLCC back-to-back, the system comprising: a new energy station, a low-frequency transmission line, a back-to-back converter station and a receiving-end power grid. The new energy station is used to generate low-frequency alternating current, which is transmitted to the back-to-back converter station through a low-frequency transmission line, wherein the back-to-back converter station comprises a rectifier station and an inverter station; the rectifier station is used to convert the low-frequency alternating current transmitted by the low-frequency transmission line into direct current, which is transmitted to the inverter station through the direct current line; the inverter station is used to convert the direct current transmitted by the direct current line into industrial frequency alternating current, which is transmitted to the receiving-end power grid.

[0006] On the other hand, the present disclosure also provides a new energy transmission method based on low-frequency SLCC back-to-back, the method comprising: generating low-frequency alternating current through a new energy station, and transmitting the low-frequency alternating current to a rectifier station through a low-frequency transmission line; the rectifier station processes the low-frequency alternating current to obtain direct current, and the direct current is transmitted from the rectifier station to an inverter station through a direct current line; the inverter station processes the direct current to obtain industrial frequency alternating current; and the industrial frequency alternating current is transmitted to a receiving power grid.

[0007] The technical solutions provided by one or more embodiments of the present disclosure can combine the technical advantages of low-frequency power transmission and direct current power transmission to achieve large-scale efficient and reliable transmission of new energy. Specifically, lower frequencies can be used to transmit electric energy, and new energy stations can directly convert electric energy into low-frequency alternating current for transmission.

[0008] It can be seen that the technical solution provided by the present disclosure can achieve the following technical effects: the new energy station of the present disclosure directly converts electric energy into low-frequency alternating current for transmission, and there is no need to establish a sending-end converter station on the new energy side. It has significant advantages for scenarios such as offshore wind power that have high requirements on the volume and weight of the platform; the rectifier-side converter station of the present disclosure uses SLCC, which has fewer flexible direct current sub-modules than the flexible direct current sub-module, and the economy is greatly increased. The system transmission capacity is not limited by the capacity of IGBT (Insulated Gate Bipolar Transistor) devices, and has stronger voltage support capabilities than conventional direct current; the present disclosure realizes the organic combination of low-frequency transmission and direct current transmission technology, and has both the high transmission efficiency of low-frequency transmission and the technical maturity of direct current transmission, and has high engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0010] Figure 1 A schematic diagram of the topological structure of a new energy transmission system based on low-frequency SLCC back-to-back in one embodiment of the present disclosure is shown; Figure 2 A schematic diagram of a topological structure of an inverter station using SLCC in one embodiment of the present disclosure is shown; Figure 3 A schematic diagram of a topological structure of an inverter station using LCC in one embodiment of the present disclosure is shown; Figure 4 A schematic diagram of a topological structure of an inverter station using MMC in one embodiment of the present disclosure is shown; Figure 5 A schematic diagram showing the control function of the SLCC of a new energy delivery system based on low-frequency SLCC back-to-back in one embodiment of the present disclosure is shown; Figure 6 A schematic diagram of the structure of SVG in one embodiment of the present disclosure is shown; Figure 7 A schematic diagram of the steps of a new energy transmission method based on back-to-back low-frequency SLCCs in one embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0012] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0013] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0014] With the continuous development of new energy power generation technology, related technologies can be used to transmit new energy over long distances through direct current transmission. Conventional direct current transmission technology and flexible transmission technology are widely used. In view of this, one or more embodiments of the present disclosure can combine the technical advantages of low-frequency transmission and direct current transmission to achieve efficient and reliable transmission of large-scale new energy. Specifically, low-frequency transmission has a lower frequency and less electromagnetic interference, which can reduce the inductance and resistance of the line, thereby increasing the transmission capacity and reducing transmission losses, and is suitable for long-distance transmission of new energy. Direct current transmission can provide stable voltage and frequency, reduce harmonic interference, and improve power quality. Therefore, combining low-frequency transmission with direct current transmission can improve the operating efficiency and power quality of the power grid and achieve efficient and reliable transmission of large-scale new energy.

[0015] In addition, in the related DC transmission technology, two converter stations are usually set at the sending end and the receiving end, and connected through a DC transmission line. In one embodiment of the present disclosure, a back-to-back converter station is set at the receiving end, and the back-to-back converter station includes a rectifier station and an inverter station. There is no need to build a converter station at the sending end, so as to achieve lightweight of the above-mentioned device and greatly improve the energy utilization efficiency.

[0016] Based on the above ideas, the present disclosure can improve the transmission capacity of the line and the utilization rate of energy on the one hand, and can also realize the lightweight of the device and adapt to more complex transmission scenarios on the other hand. The above transmission scenario can be a transmission scenario of the power system. For example, the transmission scenario can be a medium / long-distance offshore wind power transmission, onshore wind power transmission in remote areas of "Shagohuang", photovoltaic power generation transmission or large-scale hydropower transmission and other renewable energy efficient and reliable transmission scenarios.

[0017] Take offshore wind farms as an example. Offshore wind farms are usually located in sea areas far away from land and power grids. The use of low-frequency transmission can reduce transmission losses and improve transmission efficiency. In addition, the construction of offshore wind farms requires overcoming greater water depths, stronger currents and waves. Low-frequency transmission technology can provide a more stable power transmission solution. Specifically, low-frequency AC transmission can reduce electromagnetic interference to surrounding electronic equipment. Due to the lower frequency, the transmission loss of low-frequency AC may be lower than that of standard frequency AC transmission. In some cases, low-frequency AC transmission can improve transmission efficiency.

[0018] See also Figure 1In one embodiment of the present disclosure, a new energy transmission system based on low-frequency SLCC back-to-back can be provided. The topological structure of the new energy transmission system based on low-frequency SLCC back-to-back includes: a new energy station 1, a low-frequency transmission line 2, a back-to-back converter station and a receiving-end power grid 5. The back-to-back converter station includes a rectifier station 3 and an inverter station 4. The new energy station is connected to the rectifier station through the low-frequency transmission line, and the rectifier station is connected to the inverter station through a DC line. The inverter station is connected to the receiving-end power grid. The functional structure of the new energy transmission system based on low-frequency SLCC back-to-back includes: S11: The new energy station is used to generate low-frequency alternating current, and the low-frequency alternating current is transmitted to the back-to-back converter station through the low-frequency transmission line.

[0019] S13: The rectifier station is used to convert the low-frequency alternating current transmitted by the low-frequency transmission line into direct current, and the direct current is transmitted to the inverter station via the direct current line.

[0020] S15: The inverter station is used to convert the DC power transmitted from the DC line into industrial frequency AC power, and the industrial frequency AC power is transmitted to the receiving end power grid.

[0021] In this embodiment, compared with the industrial frequency system of the same voltage level, the low-frequency transmission system uses a lower frequency to transmit electric energy, and its line transmission capacity is greatly improved. In complex scenarios such as offshore wind power transmission and onshore wind power transmission in remote areas, low-frequency transmission has significant advantages in large-scale long-distance transmission of new energy. Preferably, 20Hz low-frequency AC can be used as low-frequency AC for transmission.

[0022] In one embodiment, the new energy station includes a new energy unit and a transformer. The new energy unit is not limited in the present disclosure. Optionally, taking a wind turbine for wind power generation as an example, the wind turbine converts wind energy into electrical energy, transmits alternating current to the transformer for boosting, and adjusts the voltage and frequency so that the voltage and frequency of the alternating current are adjusted to low-frequency alternating current suitable for long-distance transmission, and the low-frequency alternating current is transmitted to a transmission line.

[0023] In this embodiment, the receiving end converter station adopts a back-to-back converter station, including a rectifier station and an inverter station. Optionally, the rectifier station and the inverter station can adopt SLCC, and the SLCC converter includes a converter transformer, an LCC (Line Commutated Converter) and an SVG (Static Var Generator), which can realize self-compensation of reactive power and harmonics and maintain the stability of the transmission system. Among them, the SVG is configured with a starting circuit, and the starting circuit is configured between the connection point of the SVG and the LCC on the valve side of the converter transformer, and the starting circuit includes: an integrated current measuring device, a starting resistor and a complete starting device with a single-pole disconnector.

[0024] In this implementation, when the rectifier station adopts SLCC, please refer to Figure 5 , the converter transformer adjusts the voltage level of the received low-frequency AC power. Further, the SVG adjusts the low-frequency side voltage by emitting / absorbing reactive power. In addition, the SVG has a harmonic compensation function, thereby reducing the impact of harmonics generated by the rectifier station on the power grid and maintaining the stability of the system. Further, the LCC converts the regulated low-frequency AC power into DC power by controlling the trigger angle of the thyristor, wherein the LCC needs to consume a certain amount of reactive power, which can be provided by the SVG.

[0025] In this implementation, when the inverter station adopts SLCC, please refer to Figure 5 and Figure 2 The inverter station receives the DC power sent by the rectifier station, and the LCC converts the DC power into industrial frequency AC power by controlling the trigger angle of the thyristor. The LCC needs to consume a certain amount of reactive power. The SVG offsets the harmonics generated by the LCC by injecting compensation current. The transformer adjusts the voltage of the low-frequency AC power through taps and transformation ratios to ensure that it matches the voltage of the receiving power grid.

[0026] Specifically, the control function of the SLCC can be found in Figure 5 As shown, the rectifier side LCC adopts constant DC voltage control, and the SVG adopts constant reactive power or constant AC voltage control. The SVG adjusts the voltage of the access point by emitting / absorbing reactive power. The control system of the SLCC adjusts the output current according to the voltage value to achieve reactive power compensation. The SVG compensates for the harmonic current in the power grid by generating and eliminating harmonic currents of specified orders to reduce the harmonics generated by LCC commutation. The LCC controls the flow of reactive power and adjusts the voltage by changing the trigger angle of the thyristor.

[0027] In this embodiment, SVG compensates for the harmonics generated by the LCC of the rectifier station or the inverter station, selects the filtering order as 12n±1, and cancels the 6(2n)±1 harmonics through the upper and lower six-pulse unit transformers. Specifically, the LCC in the rectifier station and the inverter station may generate harmonics, which will affect the power quality, so SVG is selected for harmonic compensation. Among them, the filtering order of 12n±1 is selected to cancel the harmonics of a specific frequency. Here n is an integer, n=1,2,3..., 12n±1 means that the design frequency of the filter is the frequency of the 12n harmonic, that is, 12n±1 times the fundamental frequency. The 6(2n)±1 harmonics are canceled by the upper and lower six-pulse unit transformers.

[0028] Optionally, see Figure 3 In one embodiment, the inverter station can also use LCC and converter transformer. The DC voltage provided by the DC transmission line is applied to the DC side of the LCC, the control system triggers the first thyristor, and the DC current flows to the output end of the converter transformer. By continuously triggering the thyristors, the DC voltage forms an AC waveform at the output end of the converter transformer, and the output end AC voltage and current are output to the receiving end power grid. Among them, DC power is transmitted to the inverter station through the DC transmission line, and the converter transformer of the inverter station increases or decreases the voltage of DC power to a voltage level suitable for LCC operation. The LCC adjusts the output voltage and frequency by controlling the triggering angle of the thyristor to ensure that it matches the standard of the power grid. It should be noted that the voltage and frequency of the industrial frequency AC power output by the inverter station usually match the standard voltage and frequency of the local power grid.

[0029] Optionally, see Figure 4 In one embodiment, the inverter station may also use MMC (Modular Multi-Level Converter) and a transformer. When the MMC system is started, in order to prevent the switch device from being subjected to excessive voltage stress when the submodule is not fully charged, a start-up circuit is usually set when the inverter station uses MMC. The start-up circuit includes: an integrated current measuring device, a start-up resistor, and a complete start-up device with a single-pole isolating switch.

[0030] Specifically, direct current is transmitted to the inverter station through the direct current transmission line, and the converter transformer increases or decreases the voltage of the direct current to a voltage level suitable for the operation of the MMC. The MMC generates alternating current by controlling the conduction and shutdown of the insulated gate transistor and transmits it to the power grid. It should be noted that the voltage and frequency of the industrial frequency alternating current output by the inverter station usually match the standard voltage and frequency of the local power grid.

[0031] In this embodiment, the LCC includes two six-pulse thyristor rectifier units, and the two six-pulse thyristor rectifier units constitute a twelve-pulse rectifier unit. The thyristors are used to convert alternating current and direct current into each other by switching the thyristors on and off.

[0032] In this embodiment, each thyristor is triggered to turn on and off at a specified time in each AC power cycle. Specifically, the triggering of the thyristor is achieved by the control system according to the phase of the AC power. In a six-pulse bridge circuit, two thyristors will be turned on in each phase in each cycle, corresponding to the positive half-cycle and the negative half-cycle respectively. When the AC voltage passes through zero, the currently turned-on thyristor will be turned off naturally, and the next thyristor will be triggered to turn on. Due to the orderly turn-on and turn-off of the thyristors, an approximately smooth DC voltage and current will be formed on the DC side of the LCC, wherein the polarity and magnitude of the DC voltage can be adjusted by controlling the trigger angle of the thyristor, and the trigger angle is the angle from the start of the phase of the AC voltage to the turn-on of the thyristor.

[0033] In this implementation, see Figure 6 The SVG includes a three-phase star-connected branch, one of the branches includes a plurality of full-bridge sub-modules and a buffer reactor, the full-bridge sub-module is connected in series with the buffer reactor, the full-bridge sub-module is used to control the phase and amplitude of the current, generate or absorb reactive power, and the buffer reactor is used to provide a path for energy dissipation and freewheeling, and limit the peak value of the voltage.

[0034] Specifically, the full-bridge submodule includes four insulated gate transistors and a DC capacitor. The insulated gate transistors are connected in a specific way to form a full-bridge circuit, which can effectively control the phase and amplitude of the current. By adjusting the switching action of the full-bridge submodule, the SVG can emit / absorb reactive power according to the needs of the system, thereby realizing the compensation of reactive power. The DC capacitor can store energy and provide or absorb the required electrical energy when the insulated gate transistor is switched to maintain the stability of the DC side voltage and ensure the reliable operation of the SVG.

[0035] Specifically, the buffer reactor is connected to the output end of the full-bridge submodule to provide a path for energy dissipation and freewheeling for the SVG. When the SVG needs to quickly adjust reactive power, the buffer reactor can limit the peak voltage to prevent overvoltage from damaging the submodule. At the same time, during the process of current discontinuity or commutation, the buffer reactor provides a freewheeling path, reduces current discontinuity and voltage mutation, and reduces the harmonic content of the system.

[0036] In one embodiment, the MMC includes a plurality of submodules, each of which includes a capacitor, an insulated gate transistor, and a switching device. By controlling the switching state of the submodules, active power and reactive power can be effectively controlled, as well as voltage and frequency can be adjusted. Specifically, the MMC can control the flow direction and amplitude of the current, thereby achieving independent control of active power and reactive power. At the same time, by changing the waveform and amplitude of its output voltage to adjust the connected grid voltage, and by adjusting the frequency of the output voltage, the MMC can achieve frequency conversion between the AC grid and the DC grid in the DC transmission system.

[0037] It should be noted that SVG needs to be pre-charged before starting, in order to ensure that SVG can operate stably during startup and avoid impact on the power grid. The following are two common pre-charging methods: Optionally, the SVG submodule is charged by the power supply of the station. When in the system startup stage, the starting resistance of the SVG is put into operation, the isolating switch is disconnected, and the SVG of the station is charged, and the charging includes uncontrolled charging and controlled charging. When in the uncontrolled charging stage, the SVG converter valves are all in a locked state, and the submodule capacitor is charged through the diode circuit. When the capacitor voltage reaches the submodule energy extraction voltage, the submodule enters the controlled charging stage. When in the controllable charging stage, the control link actively charges the submodule capacitor, and the submodule voltage rises rapidly. When the submodule voltage reaches the rated steady-state operating voltage, the SVG enters the normal operating state, and the startup process ends.

[0038] Optionally, the station SVG can be powered. The starting resistor bypass isolation switch of the station SVG is in the disconnected state, that is, the starting resistor is put into operation. At this time, the station LCC is in the put-in state. When entering the active charging stage, the starting resistor bypass isolation switch of the bypass station SVG is in the closed state. When charging is completed, the starting resistor bypass isolation switch of the bypass station SVG is in the closed state. When charging is not required, the starting resistor bypass isolation switch of the bypass station SVG is in the closed state.

[0039] In one embodiment, the station SVG can be used to charge the station. Specifically, before starting the charging process, it is necessary to ensure that the start-up circuit of the station SVG is closed to avoid misoperation during the charging process, and the output end of the station SVG is connected to the input end of the station to form a charging circuit. The DC capacitor of the station is charged by controlling the insulated gate transistor of the station SVG. In addition, after charging is completed, it is necessary to disconnect the start-up circuit of the station SVG to ensure that the station SVG will not continue to supply power to the station after charging is completed.

[0040] In practical applications, the appropriate pre-charging method can be selected based on factors such as the capacity of the SVG and grid conditions. Generally, in order to ensure the stable operation of the SVG, the pre-charging parameters need to be designed and optimized in detail. After the pre-charging is completed, the SVG can be stably connected to the grid and play its reactive power regulation and voltage control functions.

[0041] Based on the above, the present disclosure provides a new energy transmission system based on low-frequency SLCC back-to-back, which can generate low-frequency AC power through the specific power generation mechanism of the new energy station, and the low-frequency AC power is transmitted to the rectifier station through the low-frequency transmission line. The rectifier station converts the low-frequency AC power into DC power, and the DC power is transmitted to the inverter station through the DC line. The inverter station converts the DC power into industrial frequency AC power and sends it to the receiving end power grid. Please refer to Figure 7 The present disclosure also relates to a new energy delivery method, which can be processed according to steps S31 to S37: S31: Generate low-frequency alternating current through a new energy station, and transmit the low-frequency alternating current to a rectifier station through a low-frequency transmission line.

[0042] In one embodiment, the new energy station takes a wind farm as an example. Preferably, the low-frequency AC power is selected as 20 Hz low-frequency AC power, wind energy is converted into AC power, and the AC power is processed to obtain 20 Hz low-frequency AC power, which is transmitted to the rectifier station via a low-frequency transmission line.

[0043] S33: The rectifier station processes the low-frequency alternating current to obtain direct current, and the direct current is transmitted from the rectifier station to the inverter station through a direct current line.

[0044] In one embodiment, the rectifier station includes a converter transformer and an SLCC, receives the 20 Hz low-frequency AC power, and converts the 20 Hz low-frequency AC power into DC power after being processed by the converter transformer and the SLCC. The DC power is then sent to the inverter station via a DC transmission line.

[0045] S35: The inverter station processes the DC power to obtain industrial frequency AC power.

[0046] In one embodiment, the inverter station includes a converter transformer and an SLCC, receives the DC power, and converts the DC power into 50 Hz industrial frequency AC power suitable for industrial transportation after being processed by the converter transformer and the SLCC. The 50 Hz industrial frequency AC power is transmitted to the receiving power grid.

[0047] S37: The industrial frequency alternating current is transmitted to the receiving power grid.

[0048] In one embodiment, the receiving-end power grid receives the 50 Hz industrial frequency AC power and transmits it to the user side. The receiving-end network is a power grid system that receives power generated by renewable energy or other forms of power generation.

[0049] Among them, the design and operation of the receiving power grid needs to consider many factors, including power demand, geographical location, environmental conditions, etc., to ensure the safe, reliable and efficient operation of the power grid.

[0050] Optionally, in this embodiment, the low-frequency AC power is set to 20 Hz, thereby achieving long-distance and large-capacity power transmission, and the industrial frequency AC power is set to 50 Hz industrial frequency, which is the standard frequency of industrial and civil power grids.

[0051] For the specific implementation of the method embodiment of the present application, please refer to the description of the aforementioned system embodiment, and the method embodiment can also achieve the technical effect of the system embodiment, which will not be repeated here.

[0052] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0053] The present application introduces exemplary embodiments with reference to the accompanying drawings, however, the present application can be implemented in many different forms and is not limited to the embodiments described herein, which are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0054] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0055] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the method embodiment, since it is basically similar to the system embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0056] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

[0057] Although the embodiments of the present application have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A new energy transmission system based on low-frequency SLCC back-to-back, characterized in that: include: The new energy station is used to generate low-frequency alternating current, which is transmitted to the rectifier station through a low-frequency transmission line; The rectifier station is used to convert the low-frequency alternating current transmitted by the low-frequency transmission line into direct current, and the direct current is transmitted to the inverter station through the direct current line; The inverter station is used to convert the direct current transmitted from the direct current line into industrial frequency alternating current, and the industrial frequency alternating current is transmitted to the receiving end power grid.

2. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 1 is characterized in that: The rectifier station includes a SLCC, and the SLCC includes a converter transformer, an SVG and an LCC, wherein: The converter transformer is used to achieve voltage level conversion, and the voltage of the low-frequency alternating current at both ends of the converter transformer is adjusted through taps and transformation ratios; The SVG is used to generate or absorb reactive power, adjust the low-frequency AC voltage, suppress harmonics and perform amplitude and phase correction; The LCC is used to convert the regulated low-frequency alternating current into the direct current to transmit active power.

3. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 1 is characterized in that: The inverter station includes a topology type using SLCC, and the inverter station includes a converter transformer, an SVG and an LCC, wherein: the LCC is used to convert the direct current into the industrial frequency alternating current, transmit active power, and consume reactive power; The SVG is used to generate or absorb reactive power, adjust the industrial frequency AC voltage, suppress harmonics, and perform amplitude and phase correction; The converter transformer is used to achieve voltage level conversion and adjust the industrial frequency AC voltage through taps and transformation ratio.

4. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 1 is characterized in that: The inverter station also includes a topology type using LCC, and the inverter station includes LCC and a converter transformer, wherein: The LCC is used to convert the direct current into the industrial frequency alternating current to transmit active power; The converter transformer is used to achieve voltage level conversion and adjust the industrial frequency AC voltage through taps and transformation ratio.

5. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 1 is characterized in that: The inverter station also includes a topology using MMC, wherein the inverter station includes an MMC and a converter transformer, wherein: The MMC is used to convert the direct current into the industrial frequency alternating current to transmit active power; The converter transformer is used to achieve voltage level conversion and adjust the industrial frequency AC voltage through taps and transformation ratio.

6. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 1 is characterized in that: The SVG is specifically used to compensate for the harmonics generated by the rectifier station or the inverter station LCC, and the filtering order is selected to be 12n±1, and the harmonics of 6(2n)±1 can be offset by the upper and lower six-pulse unit transformer pairs.

7. The new energy transmission system based on low-frequency SLCC back-to-back according to claim 6 is characterized in that: The SVG includes a three-phase star connection and adopts a modular multi-level commutation method, wherein: The branch includes a plurality of full-bridge sub-modules and a buffer reactor, and the full-bridge sub-modules are connected in series with the buffer reactor.

8. The new energy transmission system based on low-frequency SLCC back-to-back according to any one of claim 1, characterized in that: There are two pre-charging methods for SVG. The first method is to charge the SVG through the power supply of the station where it is located. The second method is to start the station by pre-charging. Charging the SVG submodule through the power supply of the station where it is located includes: When the system is in the startup phase, the startup resistor of the SVG is put into operation, the bypass isolation switch is disconnected, and the SVG of the station is charged. The charging includes two stages: uncontrolled charging and controlled charging. When in the uncontrolled charging stage, the SVG converter valves are all in a locked state, and the submodule capacitor is charged through the diode circuit. When the capacitor voltage reaches the submodule energy extraction voltage, the submodule enters the controlled charging stage; When in the controllable charging stage, the control link takes effect to actively charge the submodule capacitor, and the submodule voltage rises rapidly. When the submodule voltage reaches the rated steady-state operating voltage, the SVG enters a normal operating state, and the startup process ends.

9. The new energy delivery system based on low-frequency SLCC back-to-back according to claim 8 is characterized in that: Starting with pre-charging the station includes: The starting resistor bypass isolating switch of the station SVG is in the disconnected state, that is, the starting resistor is in operation, and the station LCC is in the in operation state at this time; If the active charging stage is entered, the bypass isolation switch of the starting resistor of the bypass station SVG is in a closed state; If charging is completed, the bypass isolation switch of the starting resistor of the bypass station SVG is in the closed state; If charging is not required, the bypass isolation switch of the starting resistor of the bypass station SVG is in a closed state.

10. The new energy transmission system based on low-frequency SLCC back-to-back according to claim 8 or 9, characterized in that: The starting resistor bypass isolation switch of the SVG comprises: The SLCC includes a corresponding SVG starting circuit, which includes an integrated current measuring device, a starting resistor and a complete starting device with a single-pole isolating switch.

11. A new energy transmission method applied to a new energy transmission system based on low-frequency SLCC back-to-back as described in any one of claims 1 to 10, characterized in that: The method comprises: Generate low-frequency alternating current through a new energy station, and transmit the low-frequency alternating current to a rectifier station in a back-to-back system through a low-frequency transmission line; The rectifier station processes the low-frequency alternating current to obtain direct current, and the direct current is transmitted from the rectifier station to the inverter station through a direct current line; The inverter station processes the direct current and transmits the obtained industrial frequency alternating current to the receiving-end power grid.

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